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The term homeostasis was first coined by Walter Cannon in 1929 to literally mean ‘steady state’.
It describes the dynamic equilibrium by which internal constancy is maintained within set limits by regulation and control.
Scientists studying circadian rhythms (24-hour bodily cycles) have pointed out that the internal environment does not have completely constant ‘normal’ set point.
They have found, for example, that the set point for human body temperature varies over a 24 hour cycle, fluctuating between 36°C and 37°C.Firstly, we will discuss the control of blood glucose levels in mammals, and then will look at the role of plant stomata in regulating water loss.The human body has a number of mechanisms in place to regulate the storage and release of molecules for energy.Both of these hormones are produced and released by specialised cells in the pancreas known as Islets of Langerhans.Insulin is released from β-cells, and glucagon is released from α-cells.Figure 2: Blood glucose control by insulin and glucagon If the blood glucose level is too high, more insulin and less glucagon is released.This causes cells to take in glucose from the blood, while the liver converts glucose to glycogen.As a result of this research, current thinking suggests that while homeostasis controls the ‘minute-by-minute fluctuation in the environment’ , circadian rhythms control the body’s general programming over time.In this essay, we will concentrate on two examples of homeostasis, one that occurs in humans and one which occurs in plants.The hypothalamus is a combined receptor and control centre, both recognising extremes of temperature change, and triggering bodily effectors to correct the changes.Figure 1 shows the responses to a decrease in body temperature, which directs organs to increase metabolism, thus causing shivering.